BOTANY 



Order II. Protococcoideae 



The Protococcoideae are unicellular plants distinguished from the 

 Volvocaceae by the absence of cilia in the vegetative cells. The cells 

 may be isolated, or may be united into colonies or cell-families, 

 often of characteristic form and large size. Many of them produce 

 motile reproductive cells, which are sometimes not distinguishable 

 from such Volvocaceae as Chlamydomonas. As the latter often mul- 

 tiply for a long time in a non-motile condition, it is sometimes 



E 



H 



FIG. 68. -4, Pleurococcus vulgaris : I, full-grown individual ; II, III, cells dividing. 

 B, Apiocystis Brauniana. Young colony attached to a filament of CEdogonium 

 (X 300). C, Rhaphidium polymorphum : II, cells dividing. D, Scenedesmus 

 obtusus : one of the cells has divided to form a young colony. E, &. dimorphus. 

 F, small colony of Pediastrum Boryanum. G, young colony still enclosed in the 

 membrane of the mother-cell. H, polyedrium, or resting-spore, probably of the 

 same form. (All figures except B, X about 500.) 



impossible to be sure whether a given organism belongs to the Proto- 

 coccoideae or Volvocaceae. It is extremely probable that the lower 

 Protococcoideae have been derived from the simpler Volvocaceae, by 

 the permanent loss of motility in the vegetative cells a character 

 common to all plants above the Volvocaceae. 



The Protococcoideae are mainly fresh-water plants, growing either 

 completely submersed, or simply in moist places, on shaded earth, 

 trunks of trees, roofs, etc. A few of them grow associated with 

 other organisms. The green color of certain animals fresh-water 



